Apparatus and method for purifying air

ABSTRACT

An apparatus and method of purifying air where a photocatalyst is exposed to ambient air to purify it from bacteria, hydrocarbons, and volatile organic compounds. The apparatus can contain a vertical reactor containing the photocatalyst either on sheets, in a web-like structure, or in a fibrous mass, or any other way of holding it. The photocatalyst can be excited with an ultraviolet light source. Air rises through the reactor by natural convection caused by a heater or heater element located in the reactor. The apparatus can contain no moving or replaceable parts. An optional air filter can also be located at the bottom of the reactor to remove particulate matter from the rising air. In one embodiment, excess visible light from the ultraviolet light source is allowed to escape from the top, bottom, or side of the device to provide light for persons to see at night thereby acting as a night light which simultaneously purifies air. The invention also comprises a method where cooler ambient air is allowed to enter a chimney or reactor and flow upward past a heater by natural convection, also flowing past an excited photocatalyst thereby being purified from contaminants such as bacteria and organic compounds.

BACKGROUND

1. Field of the Invention

This invention relates generally to the field of air quality and moreparticularly to an apparatus and method for purifying air.

2. Description of Related Art

Air purifiers generally consist of filter units driven by fans. Thefilters may be particulate filters followed by activated charcoal orother filter types. In general, the fans are noisy, and the filters needoften replacement.

Some devices have been built using photocatalysts activated byultraviolet light. In general these have been wall panels, or filterdevices again driven by fans. U.S. Pat. No. 5,919,422 teaches a numberof configurations where ambient air in a container simply reacts withthe photocatalyst by diffusion. This method will work for a smallcontainer, but needs the addition of a fan to purify air in an entireroom. U.S. Pat. No. 5,945,372 teaches a photocatalyst used in buildingHVAC systems (with large fans) to purify air in buildings.

What is badly needed is a small device that can be directly plugged intoa wall electrical socket that contains no moving or replaceable parts.This device should, over a period of hours, purify the air in a room bykilling bacteria, removing organic compounds, and possibly evenconverting poisons such as carbon monoxide into something more harmlesssuch as carbon dioxide. The device must be quiet, since it would be leftin a room both day and night. Its purifying element must never needreplacement. It must not produce too much heat, and it should not needany maintenance.

SUMMARY OF THE INVENTION

The present invention relates to an apparatus and method for purifyingair in a room. The invention causes air to pass through a verticalpassageway or chimney (reactor) that contains a photocatalyst that isactivated by an ultraviolet light source. Air is caused to move by aprocess called natural convection whereby no external force such as afan needs to be used. Natural convection occurs when air is heated by ahot body and hence becomes less dense than colder surrounding air. Theless dense air experiences an increase in upward buoyancy force whichcauses it to move upward. The present invention can contain a smallheater or heat element in a vertical passageway or chimney (reactor).Cold air can enter the apparatus through slots or openings at the bottomof the device. An optional filter can be placed here to removeparticulate matter. A heater or heat element can be placed above the airentrance port or filter if a filter is present. This heater causesnatural convection to take place. As the warmer air moves upward, apressure gradient is formed which in turn draws more cool air into thedevice.

The slightly heated air passes up through the chimney or reactorpassageway where it encounters a photocatalyst such as titanium dioxideeither in pure form or doped with any of several metals. Thephotocatalyst is activated by an ultraviolet light source that emitslight with a wavelength or spectrum shorter than 387 nanometers (whichis the activation energy of pure titanium dioxide in the anatase crystalform), or shorter than the activation energy of whatever catalyst isused.

The photocatalyst is held in the chimney in a form which exhibits alarge surface area to allow maximum exposure of the air that isconvecting upward. The photocatalyst can be coated on a flat sheet whichin turn can be spiraled on a loose spool to obtain more surface area ofexposure, or the photocatalyst can be impregnated on fibers which can beformed into a fibrous mass (an example of such fibrous mass might befiberglass insulation or a like fiber). The fibers can be natural orsynthetic organic materials, or can be glass such as fiberglass. Anymeans of holding the photocatalyst in position so that air passingupward in the chimney makes contact with it is within the scope of thepresent invention.

The ultraviolet light source that is used to activate the photocatalystcan be a commercial UV light bulb, a fluorescent lamp (which leaksconsiderable UV light), or a means of allowing sunlight to enter thedevice. If a UV bulb is used, an optional power supply usually must beused to supply the bulb voltage.

The present invention contains an exit port on its top which can beslots or a small jet to allow the upward convecting air to re-enter theroom. This port can contain an optional baffle to prevent UV light fromentering an observer's eyes. This type of protection is necessary ifwavelengths shorter than about 340 nanometers are used. It may also bedesirable in some cases to prevent any visible light produced by the UVsource from exiting the device. In other cases, it may desirable toallow visible light to exit the device so that the present invention canalso be used as a night light while it purifies the air.

The present invention can be equipped with two electrical prongs on itsback side so that it can be directly plugged into a standard 110 V.electrical outlet, or, optionally, it can have a power cord. Power fromthe electrical outlet can be used to supply energy to both the heaterand to the ultraviolet light source. The direct electrical connection isoptional since the present invention can also be run directly frombatteries.

The present invention purifies air in a room over a span of hours sincethe rate of natural convection is slow. The invention can kill bacteriaand can convert organic compounds such as volatile organics (VOC's),odor causing organics, hydrocarbons, and other undesirable compoundsinto smaller, less harmful or odorous, compounds such as carbon dioxide,water.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of an embodiment of the presentinvention. Electrical prongs are clearly seen.

FIG. 2 shows a cut-away diagram of the interior of a particularembodiment.

FIG. 3 shows an embodiment of the present invention as it is used topurify air in a room.

FIG. 4 shows a corrugated tube means for holding catalyst.

FIG. 5 shows a fibrous mass holding catalyst.

FIG. 6 shows catalyst attached to a plate.

FIG. 7 shows catalyst in tubes in a structure.

FIG. 8 shows an embodiment equipped with an elongated chimney orreactor.

DETAILED DESCRIPTION

Turning to FIG. 1, a perspective view of one embodiment of the presentinvention is seen. The unit can be made small enough to plug directlyinto an electrical outlet. The unit can contain electrical power prongs4 on its backside for this purpose. Of course, it could be equipped witha power cord for normal plug-in. I could also use a wall plugtransformer with a low voltage cord to the unit, or it could usebatteries.

The unit can be housed in a plastic shell 1 for lightness andappearance. The shell or enclosure can however be any materialincluding, but not limited to, plastic, wood, metal, or any other rigidmaterial. Several holes or slots 3 can be provided on the top of theunit for purified air to exit the invention. These can be holes, slots,a nozzle, or any other means for air to exit the enclosure 1. The unitis also provided with slots, a hole, or any other means for contaminatedair to enter the enclosure at the bottom. This entrance port 5 cannot beseen in FIG. 1.

The power prongs 4 can be directly connected to a power module or powersupply 2. While this module 2 is shown external to the enclosure 1 inFIG. 1, it should be noted that this power supply or module can beinside the enclosure 1 so that the back of the unit is flat.

FIG. 2 shows a cut-away diagram of the interior of an embodiment of thepresent invention. The electrical prongs 4 and power module 2 are againseen. Contaminated air can enter the bottom the unit through slots orany type of entry port of entry means 5. A heater pad 7 heats this air,and the air rises by natural convection. The heater pad 7 can be porusor permeable, or made in a type of weave so that air can readily passthrough it. FIG. 2 shows holes or passageways 10 in the heater pad 7.Actual holes or passageways are not necessary if the pad is porus orpermeable or a weave. The heater pad is attached to the power module 2by a set of wires 12 that supply it with power. Any type of heater iswithin the 'scope of the present invention; however, the preferredheater supplies a constant flow of heat energy maintaining a surfacetemperature between 40 degrees C. to 70 degrees C. While hotter pads canbe used, they can present a danger of fire, or a danger of heating theair hot enough that it might cause a burn if a person were to put theirhand in the flow, etc. Also, since the purpose and objective of thepresent invention is to purify air over a prolonged period, it is notnecessary to heat the air too hot in order to sufficiently purify theair in a room.

An optional filter 13 can be provided in the reactor to remove largerparticulate matter. It should be noted that such a filter is anadditional feature, and is not required for the functioning of thepresent invention. The enclosure 1 forms a chimney for the upward airflow. An internal chimney can be used if it is necessary to moreaccurately direct the flow; however, this may not be necessary. In thischimney, is a photocatalyst 8 that is either impregnated on a surface,or is attached to a fibrous mass of material. It is very important forthe photocatalyst to display a large surface area to the upward airflow. The most common photocatalyst is titanium dioxide (TiO2). The mostconvenient form of TiO2 is the anatase crystal form; however, the rutileform can be used. It is well known that the rutile form does not displayas much surface area as the anatase form. While TiO2 is the preferredphotocatalyst, any other photocatalyst capable of killing bacteria anddecomposing organic molecules is within the scope of the presentinvention.

The photocatalyst can be doped to increase its efficiency or it can beused in its pure form. The most common doping material is platinum (Pt)metal; however, numerous other dopants are known in the art. It is alsoknown that TiO2 becomes more efficient in the presence of a hydroxyl ion(OH—). It is within the scope of the present invention to use a means ofmaintaining a humidity of 40% or higher; however, it is highly desirableto avoid such a device since one of the objectives of the presentinvention is a unit that never needs servicing. TiO2, works well whenphoto-excited to kill bacteria and convert organic compounds athumidities as low as 30%, especially if it is doped.

In the region of the chimney 1, where the catalyst is exposed to the airrising past its surface by natural convection, is an ultraviolet (UV)light source 9. The activation energy of pure anatase TiO2 is 387nanometers; thus, any ultraviolet source can be used that supplies lightwith wavelengths shorter or equal to 387 nanometers (or alternativelyshorter than the activation energy of any catalyst that is used). It iswell known in the art, that commercial black lights, and even commercialfluorescent bulbs of various colors emit a considerable amount of UVlight down to about 350 nanometers. This light is highly suitable toexcite the photocatalyst 8 in the present invention and is safe to humaneyes. Shorter wavelengths can be used; however, if shorter wavelengthsare used, suitable eye protection should be provided. FIG. 2 shows a setof light baffles 11 that are present simply to protect eyes if shorterwavelengths are used. These optional baffles 11 can also be used toprevent the escape of visible light if desired.

In one embodiment of the present invention, the baffles 11 are notpresent, and a UV light source 8 of wavelength no shorter than around350 nanometers is used. The visible portion of the source's output ispurposely allowed to escape from the top or side of the device so thatthe device can be used as a night light, for example in a bathroom,while simultaneously purifying air.

Purified air, after having passed the photocatalyst 8 can escape fromthe top of the unit by either slots 3, or a nozzle 6 or any other meansof escape. Generally, only one of these escape means will be used;however, any combination can be used if needed.

An optional feature, which is usually not necessary, is a means forcontrolling humidity 24 of the air passing the photocatalyst. This canbe a small reservoir and wick, or any other means of increasinghumidity.

FIG. 3 shows an embodiment of the present invention 15 plugged into anelectrical outlet (behind the device) in the corner of a room 14. Thedevice provides a method of purifying air by heating it at the bottom ofthe enclosure so that it rises by natural convection up through thedevice passing a photo-excited photocatalyst and then back into the roomfrom the top of the device. An optional window 16 can be provided on thefront, top, or side of the device to allow visible light to also exitthe device. The present invention thus can plug into any convenientpower outlet, and immediately begin purifying air in the room, removingodors, volatile organics, and other chemicals, as well as killingairborne bacteria. In addition, as mentioned, in some embodiments of theinvention, visible light is allowed to escape so that the device alsofunctions as a night light.

FIG. 4 shows a means for containing the photocatalyst in a corrugatedtube or container 18. The shape shown in FIG. 4 is a cylinder; however,any shape is within the scope of the present invention. Here thecross-section 17 contains a honeycomb of tubes or cells which havecatalyst coated or otherwise attached to their walls. Any means ofattaching the catalyst is within the scope of the invention. Discretetubes can be used with catalyst coated on the inside and outside. Forthis embodiment, light must shine into the tubes or honeycomb to excitethe photocatalyst.

FIG. 5 shows catalyst impregnated into a fibrous bundle 19 made of finestrands of material. The strands can be any rigid material or fibercapable of being made into strands. One material that can be used isfiber glass. Another possible material is paper with the photocatalystimpregnated into its fibers. In this case, the rising air passes throughthe paper and is purified as it contacts the excited photocatalyst. Inthis case, the principle is similar to a paper filter.

FIG. 6 shows catalyst 21 attached to the surface of a plate 20. Anymethod of attachment can be used and is within the scope of the presentinvention including, but not limited to, plating, attaching withadhesive, impregnating, sputtering, diffusing, or any other attachmentmethod. The plate 20 can be metal, plastic, wood, glass, paper or anyother rigid or semi-rigid material. While a plate is shown in FIG. 6,the catalyst can be attached to a very thin sheet, and to increasesurface area, that sheet can be rolled into a loose spiral or any othershape, shapes being chosen to maximize exposed surface area.

FIG. 7 shows a system of tubes 23 in a structure 22. The tubes can becoated with catalyst on either the inside, the outside, or both theinside and outside. Any method of attaching the catalyst to the tubesurface is within the scope of the present invention, and any type ormaterial of tube is within the scope of the present invention.

FIG. 8 shows an embodiment of the present invention that is considerablytaller (extends more vertically) than other embodiments. This embodimentalso contains an outer case 1 and a means on its top for heated,purified air to escape 3. Again the optional power prongs 4 and anoptional power supply 2 can be seen. The difference between thisembodiment and the on shown in FIG. 1 is that with a taller chimney orreactor, more photocatalyst can be exposed to the rising air (the airstays in the vicinity of the catalyst for a longer period of time beforeexiting the device). A unit such as that shown in FIG. 8 purifies airfaster than a smaller unit. In all other respects, the embodiment shownin FIG. 8 is similar to that shown in FIG. 1.

It should be noted that the embodiments disclosed are for purposes ofillustration of the principles of the invention. Many other embodimentsand realizations may be made without deviating from the scope of thepresent invention. Many materials can be substituted for the ones namedin the disclosed embodiments; any material with similar properties tothe one disclosed is within the scope of the present invention.

I claim:
 1. A device for purifying air comprising: a reactor; aphotocatalyst located in said reactor; an ultraviolet light sourcelocated in said reactor, said ultraviolet source illuminating saidphotocatalyst; a heater means located in said reactor for drawing airinto said reactor by convection and causing said air to rise past saidphotocatalyst before being expelled.
 2. The device for purifying air ofclaim 1 further comprising a pair of electrical prongs protruding fromsaid device, said electrical prongs allowing said device to be directlyplugged into an electrical outlet.
 3. The device for purifying air ofclaim 1 wherein said photocatalyst is primarily titanium dioxide.
 4. Thedevice for purifying air of claim 3 wherein said titanium dioxide isdoped with a dopant.
 5. The device for purifying air of claim 4 whereinsaid dopant is platinum.
 6. The device for purifying air of claim 1further comprising a means for controlling humidity in said reactor. 7.The device for purifying air of claim 1 further comprising a fibrousmass located in said reactor, said fibrous mass holding saidphotocatalyst.
 8. The device for purifying air of claim 7 wherein saidfibrous mass is fiber glass.
 9. The device for purifying air of claim 1wherein said ultraviolet light source emits light of wavelength shorterthan 387 nanometers.
 10. A compact device with a base and a top forpurifying air that is plugged directly into a wall power outletcomprising a set of power prongs protruding from the device for plugginginto the wall outlet, a compartment containing a photocatalyst that isilluminated by an ultraviolet light source, an opening at the base ofthe device for air to enter, a heater means in the device near thisopening for heating air entering the device and causing this air to risepast the illuminated photocatalyst, the air becoming purified, and anexit port at the top of the device for the purified air to exit.
 11. Thecompact device of claim 10 where the photocatalyst is primarily titaniumdioxide.
 12. The compact device of claim 11 where the titanium dioxideis doped with platinum.
 13. The compact device of claim 11 where theultraviolet light source emits light of wavelength shorter than 400nanometers.
 14. The compact device of claim 13 where the ultravioletlight source emits light of wavelength longer than 350 nanometers, thelight source also producing visible light.
 15. The compact device ofclaim 14 further comprising a means for allowing the visible light toescape.
 16. A device for purifying air comprising: a chimney with a baseand top; a photocatalyst located in said chimney; an ultraviolet lightsource located in said chimney, said ultraviolet source illuminatingsaid photocatalyst with ultraviolet light of wavelength shorter than 387nanometers, said ultraviolet light source also producing visible light;a heater means located at the base of said chimney for drawing air intosaid chimney by convection and causing air to rise past saidphotocatalyst, said air being expelled from the top of said chimney; ameans for allowing said visible light to escape from said chimney.